Whiffle tree boom rotating mechanism for articulated aerial device



Oct. 28. 1969 w. A. PRESCOTT 3,474,682 'NHlFFLE TREE BOOM ROTATING MECHANISM FOR ARTICULATED AERIAL DEVICE Filed April 11. 1'96" 2 Sheetsr-Sheet 2 INVENTOR WIlham A. Prescorr ATTORN I9.

United States Patent Int. Cl. 1366f 11/04; F16h 27/02 US. Cl. 7489.2 18 Claims ABSTRACT OF THE DISCLOSURE Hydraulic cylinder powered, cable driven boom rotating mechanism for rotating the upper boom section of an articulated aerial boom relative to the lower, truck mounted boom section. The mechanism includes a pair of side-by-side piston and cylinder assemblies interconnected with a pair of side-by-side cables by a whifile tree arrangement. The cables are looped around a sheave rotatably mounted on the outer end of the lower boom section and rigid with the upper boom section for rotating the latter through an arc of 270 in response to extension and retraction of the hydraulically actuated pistons. Each of the boom sections includes a nonconductive portion for electrical isolation.

CROSS REFERENCE This is a continuation-in-part of my copending application Ser. No. 579,299, filed Sept. 14, 1966, now abandoned, and entitled Whiffie Tree Boom Rotating Mechanism for Articulated Aerial Device.

This invention relates generally to boom-rotating mechanisms for articulated aerial devices and, more particularly, relates to hydraulically actuated, cable-driven, boom-rotating mechanisms.

Aerial devices are especially useful for lifting personnel as well as heavy objects to relatively high levels, but such devices must be designed to preclude malfunctioning and the consequent fall of the workman or dropping of heavy loads on objects and persons below. When such devices are utilized for lifting a workman to an elevated position, the problem is particularly acute because personal injury to the workman is a virtual certainty if the mechanism fails.

Hydraulically actuated devices have been utilized with increasing regularity because they are economical to produce, provide flexibility of design, and are relatively safe to operate. Furthermore, flexible cable may be used for actuation of the components thereby providing an inherent safety factor in the design, since excessive stress on a cable normally initially causes only a few of the strands to rupture rather than the entire cable, thus providing a visual indication of cable weakness.

It has been found that a closed loop cable configuration is desirable; however, such configuration is not readily adaptable for single cylinder operation because the cylinder cannot be aligned with the direction of travel of the cable and thus must be offset far enough to clear the cable. Hence, a moment is applied through the offset linkage and the linkage and the piston rod, as well as the cable, are subjected to twisting forces which decrease the life span of the same.

Aerial devices of the type described are often utilized for repair and maintenance of live electrical transmission lines. With proper insulation, it is possible for a workman to work on high voltage lines. It is desirable to include as much insulation as possible to provide a maximum amount of safety factor; however, the length of the stroke of the hydraulic cylinders utilized for moving the boom rotation cables limits the amount of insulation for a given boom length because the cables and cylinders are generally of electrically conductive material and the length of the cylinder and its extended piston rod, or in other Words, a distance approximately equal to twice the stroke of the rod is not available for insulation purposes.

It is, therefore, the primary object of the instant invention to provide a cable-operated, hydraulically driven boom-rotating mechanism for an aerial device including structure suitable for rendering the device capable of optimum performance without substantially endangering workmen utilizing the device and without substantial increase in the overall production cost of the device as compared with previous units.

It is a very important object of the invention to include a pair of side-by-side hydraulic actuators coupled to a common cable drive structure whereby, upon failure of one actuator, the other actuator will maintain the boom in a fixed position. In this respect, it is a very important aim to provide such side-by-side actuators disposed on opposite sides of the cable whereby the moments applied on the linkage by the actuators are directly opposed and twisting of the piston rods, the linkage and the cable is substantially precluded.

An extremely important object of the present invention is the provision of cable drive structure which permits utilization of a smaller diameter boom rotation sheave than has heretofore been possible whereby the linear displacement of the cable for rotating the sheave and thereby the outer boom through a predetermined arc is minimized and the stroke of the piston rod is correspondingly decreased to the end that an additional length of boom is available for insulation purposes.

Another very important object of the present invention is the provision of a whifile tree configured common drive structure for an aerial device using a pair of actuators so that the tensile strength of the cable may be borrowed to help support the load in a static position after failure of one cylinder whereby neither cylinder must necessarily be of suflicient size to support the load unaided.

Yet another very important object of the instant invention is to provide a whiflie tree configured drive structure for an aerial device utilizing a pair of actuators to the end that compensation for the forces exerted on the structure by unevenly loaded actuators will be accomplished automatically.

Still another important object of the present invention is the provision of a cable and sheave assembly for rotating a boom about one end thereof wherein the cable is wrapped around the sheave for approximately 540 and wherein means are provided for preventing relative shifting to occur between the sheave and a portion of the cable whereby the boom may be rotated through an arc of about 270.

A further important object of the invention is the provision of a common drive structure for transmitting the forces applied by a pair of parallel hydraulic cylinders onto a flexible cable wherein the cable and the cylinder drive members are pivotally connected to the structure and arranged thereon in a manner to cause the structure to rotate upon failure of one cylinder to apply as much force on the structure as the other cylinder, whereby the unequal forces are automatically compensated for and upon complete failure of one cylinder, the mechanism locks preventing dropping of the load.

In the drawings:

FIGURE 1 is a side elevational view of a mobile articulated aerial device having boom-rotating mechanism constructed in accordance with the principles of the instant invention;

FIG. 2 is an enlarged, side elevational view of the relatively rotatable booms and rotating mechanism shown in FIG. 1, certain parts having been broken away for increased clarity;

FIG. 3 is a bottom plan view of the booms and mechanism illustrated in FIG. 2;

FIG. 4 is a top plan view of the booms and mechanism depicted in FIGS. 2 and 3; FIG. 5 is an enlarged, detailed, sectional view taken along line 5-5 of FIG. 2;

FIG. 6 is an enlarged, detailed sectional view taken along line 6-6 of FIG. 3;

FIG, 7 is an enlarged, detailed sectional view taken along line 77 of FIG. 8;

FIG. 8 is an enlarged bottom plan view of the whiflie tree plate shown in FIG. 3, illustrating the manner in which the plate pivots in response to unequal forces being applied thereon by the hydraulic cylinders; and

FIG. 9 is an enlarged, cross-sectional detail view taken along line 99 of FIG. 1.

An articulated aerial device embodying the priciples of the instant invention is illustrated in FIG. 1 and designated by the numeral 10. Device 10 has a pair of relatively rotatable boom elements 12 and 14 carried by a truck broadly designated by the numeral 16, or other similar vehicle.

Hydraulic actuation mean in the nature of a pair of piston and cylinder assemblies 18 and 20 extend longitudinally of boom element 12 therebeneath and are generally parallel with respect to the lower surface 12a of boom element 12. The piston and cylinder assemblies 18 and 20 are disposed in side-by-side relationship, A pivot mechanism 22 mounts assembly 18 on boom element 12 for rotation about an axi extending generally normally with respect to surface 12a, and a similar pivot mechanism 24 mounts the assembly 20 on boom element 12 for rotation about an axis substantially parallel to the axis of rotation of assembly 18. Assembly 18 has a reciprocable member in the nature of a piston rod 26 and assembly 20 ha a similar rod 28. The pair of rods 26 and 28 are disposed in side-by-side relationship for extension and retraction in a generally longitudinal direction with respect to boom element 12.

Upper boom 14 includes a length 14a of insulative material such as glass reinforced polyester to protect a workman in bucket 15 while working on high voltage electrical transmission lines. Toward this end, boom element 12 has a pair of spaced, longitudinally aligned end portions 17 and 19 and an insulative section 21 interconnecting the end portions 17, 19. The spacing between portions 17 and 19 is preferably at least six inches. Section 21 is constructed of glass fiber reinforced synthetic resin such as polyester and supplements the protection provided by length 14a. Nut and bolt means 23 rigidly connect section 21 and portion 19 together as can be seen viewing FIG. 9 and it is to be understood that similar (not shown) rigidly connect section 21 and portion 17.

A common structure in the nature of a whifile tree plate 30 is located at the free ends of the rods 26 and 28.

'Plate 30 has an elongated, central portion 30a which extends longitudinally with respect to boom element 12, a laterally extending portion 30b disposed for mounting rod 28, and another laterally extending portion 30c disposed 4 for mounting rod 26, Portions 30b and 30c extend equally in opposite directions on either side of the central portion 30a. Pivot means in the nature of a pair of separate pivot mechanisms 32 mount rods 26 and 28 on a respective portion 30c or 30b for rotation about axes which are generally parallel with the axe about which the assemblies 18 and 20 pivot on boom element 12.

A pair of opposed bearing mounts 34 are disposed on either side of portion 17 of boom element 12 for rotatably mounting a pulley shaft 36 for rotation of the latter about an axis extending generally horizontally through portion 17. An idler pulley 38 is mounted coaxially on shaft 36 for rotation therewith. Sheave means or mechanism including a sheave 40 is disposed at the right-hand end of portion 17 for rotating boom elements 12 and 14 relative to one another about a generally horizontal axis. Sheave 40, as can be seen viewing FIG. 5, includes a hub 42, a central, annular web 44 extending radially outwardly from hub 42, and an annular drum 46 mounted on the outer peripheral edge of web 44. Hub 42, Web 44 and drum 46 define the margins of a pair of opposed, annularly extending spaces 48 disposed on either side of web 44. A slot 50 extends laterally across drum 46, and another similar slot 52 spaced circumferentially around sheave 40 from slot 50, also extends laterally across drum 46. Drum 46 has an outer, annular surface 54 extending circumferentially around sheave 40 and being interrupted only by the slots 50 and 52.

Sheave 40 has a pair of bearing surfaces 56 aligned coaxially with drum 46, and a flange 58 spaced from drum 46 for rotation therewith about a common axis. A pair of bearing housings 60 are disposed at the right-hand end of boom element 12 and receive bearing surfaces 56 therein for permiting sheave 40 to rotate on portion 17 of boom element 12 substantially coplanarly with respect to idler pulley 38. A flange 62 mounted rigidly on boom element 14 is disposed in mated relationship with respect to flange 58, and the flanges 58 and 62 cooperate to cause boom element 14 to rotate with the sheave 40.

A pair of circumferentially spaced walls 64 are disposed within each space 48 between slots 50 and 52. Each of the walls 64 extends radially between hub 42 and drum 46 defining a chamber 66.

Flexible means in the nature of a pair of wire cables 68 has a stretch 70 extending toward idler pulley 38 from plate 30 and a stretch 72 extending toward sheave 40 from plate 30. A pivot structure 74 mounts stretch 70 on plate 30 for rotation about an axis extending substantially parallel to the axes of rotation of rods 26 and 28 about plate 30 as can be seen in FIG. 6. The free ends of the cables comprising stretch 72 extend through a cable block 76 as best illustrated in FIGS. 7 and 8. Block 76 has a tab 78 mounted on plate 30 by pivot means 80 for permitting rotation of stretch 72 relative to plate 30 about an axis substantially parallel to the axis of rotation of stretch 70 relative to plate 30. It is to be noted that disposition of the pivot mechanisms 22, 24, 32, 74 and 80 permit assemblies 18 and 20 to pivot on boom element 12, and stretches 70 and 72 and rods 26 and 28 to pivot on plate 30 about mutually substantially parallel axes.

The total cross-sectional area of the flexible means 68 determines the load-carrying capacity of the bucket 15 of device 10. That is to say, the tensile strength of the flexible means 68 is determined by the cross-sectional area thereof. Since the cross-sectional area is a function of diameter, the diameter of cables 68 is less than would be the diameter of a single cable used to replace cables 68. The minimum radius of bend of a cable undergoing continual flexure has been found to be a function of the diameter of the cross section of the cable and thus, it has been discovered that by using a plurality of side-by-side cables such as cables 68, the minimum radius of bend of the flexible means is reduced and thus the diameter of sheave 40 is correspondingly held to a minimum.

During the rotation of sheave 40 and thereby boom element 14 through an arc of 270, the linear travel of flexible means 68, which rests on the periphery of sheave 40, is determined by the relationship L=%1r(D+d), where L represents said linear distance, d represents the diameter of cable 68 and D represents the diameter of the sheave. Hence, the smaller the diameter of sheave 40, the shorter the distance L. Manifestly, L also equals the stroke of assemblies 18 and 20 for effecting 270 rotation. By utilizing a plurality of cables 68, the stroke of assemblies 18 and 20 has been elfectively decreased.

Stretches 70 and 72 are interconnected, presenting a pair of continuous cables. Block means in the nature of a pair of separate blocks 82 are swedged onto respective cables 68 at the zone of interconnection between stretches 70 and 72. Each block 82 is disposed in a respective chamber 66 between the walls 64 and web 44 and drum 46 present cable directing means for maintaining the cable 68 in double-looped relationship with respect to sheave 40 and for maintaining the blocks 82 between a respective pair of walls 64.

Viewing FIG. 2, stretch 70 extends to the left from plate 30 and wraps around pulley 38 into turnbuckle means 84. Stretch 70 continues rightwardly from turnbuckle 84 into engagement with drum 46. Stretch 70 extends along surface 54, through slot 52, through space 48, and into the chamber 66 and block means 82. Stretch 72 extends rightwardly from plate 30 around surface 54 of drum 46, then through slot 50 and space 48 into chamber 66 and block 82 on the opposite side of the latter with respect to stretch 7 0. Block 82 is captive within chamber 66 between walls 64 and a pull to the left on stretch 72 will cause sheave 40 to rotate in a clockwise direction. Although FIG. 2 illustrates the relative position of boom 14 in its extreme counterclockwise direction, it will be apparent to one skilled in the art that, if the boom had been previously rotated in a clockwise direction, that a rightward movement of plate 30 by rods 26 and 28, would exert a force on stretch 70 causing sheave 40 to rotate in a counterclockwise direction.

Operation of the device results from the application of fluid pressure on either side of a piston 86 depicted schematically in FIG. 3. Of course, it is understood that a similar piston is included in the other assembly 20. Fluid pressure exerted on the right-hand side of piston 86 will cause rod 26 to be retracted into cylinder 18 and rod 28 will be retracted into cylinder 20 in a similar manner. Conversely, pressure exerted on the left-hand side of the pistons will cause the rods 26 and 28 to be extended. Extension of the rods 26 and 28 causes plate 30 to move to the right, thus putting stretch 70 into tension and causing sheave 40 and boom element 14 to rotate counterclockwise. Likewise, when rods 26 and 28 are retracted, plate 30 will be shifted to the left, thus putting stretch 72 into tension and causing sheave 40 and 'boom element 14 to rotate in a clockwise direction.

Plate 30 and the location of the pivot mechanisms 32, 74 and 80 thereon, provide automatic compensation to permit the cable 68 to be driven by unequally loaded cylinders 18 and 20. It is to be understood that the unequal loading may be caused by various reasons such as unequal pressure in the cylinder or dissimilar frictional resistance between the piston and the cylinder wall. When equal forces are applied on plate 30 by rods 26 and 28, plate 30 will remain in the position shown in dashed lines in FIG. 8. Assuming that rods 26 and 28 are being retracted, viewing FIG. 8, and that rod 28 is exerting more force on plate 30 than rod 26 of the respective forces acting on plate 30 will cause the latter to rotate about the loaded pivot mechanism 80 to move into the position shown in solid lines. Thus, the action arm through which the force transmitted by rod 28 is acting will be reduced by the distance E, and the length of the action arm through which the force exerted by rod 26 acts is increased by the distance F. Also, a lateral increase in the length of the cable in an amount G is transmitted as elastic load through the full length of cable to loaded 6 pivot mechanism 80. The total effect of the factors mentioned will reduce the force against which rod 26 must act, and increase the force against which rod 28 must act, until a balance point is reached whereby both cylinders will cooperate at nearly uniform rate of speed to exert force on the cable 68.

Assuming that stretch 72 is in tension maintaining a load In elevated position, and piston and cylinder assembly 18 fails completely thus reducing the force applied by rod 26 on plate 30 to zero, the location of the pivot structures 32, 74 and on plate 30 will cause the cable to lock in position sufiiciently for the force exerted by rod 28 to maintain the load in fixed position and prevent device 10 from dropping the load. Again, viewing FIG. 8, plate 30 will shift into a position as illustrated by the solid lines, thus exerting a lateral increase in the length of the cable in an amount G. The resistance of cable 68 to lateral stretching results in a force vector being applied to pivot mechanism 74. This force is transmltted through the cable system at a reduced amount by the capstan effect, resulting in a resultant force vector directed for aiding rod 28 in the supporting of the load.

FIGURE 2, as mentioned above, shows the boom 14 and sheave 40 in the extreme counterclockwise positions of the same. As rods 26 and 2-8 cooperate to shift plate 30 toward the left, sheave 40 and boom element 14 will be rotated in a clockwise direction. It is to be noted that cable 68 is wrapped around sheave 40 for approximately 540. Thus, sheave 40 and boom element 14 are permitted to rotate through an arc of at least 270 while block 82 remains in position within chamber 66 and between walls 64 maintaining at least a portion of cable 68 in fixed relative relationship with respect to sheave 40.

It is to be noted that the ends 18a and 20a of assemblies 18 and 20 respectively are disposed at the end 17a of portion 17 so that the effective length of the space between portions 17 and 19 is not shortened by virtue of assemblies 18 and 20 overlapping section 21. The length of portion 17 is thus determined by the stroke of assemblies 18 and 20. It can be seen that all of the metallic components for rotating boom element 14 relative to boom 12, including assemblies 18 and 20, sheave 40, flexible means 68 and whilfle plate 30 are disposed at least as far from portion 19 as the proxirnal end 17a of portion 17. Because the flexible means includes a plurality of wire cables 68, the stroke of assemblies 18 and 20 has been reduced and the length of portion 17 has correspondingly been held to a minimum. Thus, for a given length of boom 12, additional room has been provided for the inclusion of the insulative section 21.

In devices, such as 10, embodying the principles of the instant invention, the provision of a dual piston and cylinder assembly for causing a cable to operate to swing a boom element about a horizontal axis decreases the chances that a load carried at the end ofthe boom element will be dropped. The provision of a common drive structure such as the plate 30 causes the cylinders to apply force to the cable evenly and permits the cylinders to be of minimum size because the plate will operate to cause the system to lock upon failure of one cylinder by aiding the other cylinder in maintaining the load in position. This locking occurs by virtue of the whiflle tree plate configuration and the pulley arrangement which cooperate to create a capstan eff Additionally, the inventive concepts embodied in the construction of the sheave 40 and the relationship between the sheave 40 and the cable 68 permit the sheave 40 and the boom element 14 to be rotated through an arc of 270 while maintaining at least a portion of e cable 68 in fixed relative relationship with respect to the sheave at all times.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In an articulated aerial device having a pair of relatively rotatable boom elements, the combination with said boom elements of:

hydraulic actuation means having a pair of side-by-side reciprocable members and carried by one of said boom elements;

a common structure pivotally joined to the members for reciprocable movement therewith upon simultaneous actuation of the members; and

flexible means coupled to said structure intermediate the members and operably joined to the other boom element for effecting rotation of the latter in response to movement of the structure by the hydraulic means.

2. The invention of claim 1, wherein said flexible means includes a cable having a pair of stretches, each stretch being coupled to said structure intermediate the members and located for alternately being put into tension as the structure moves in one direction and then another direction, said stretches being operably joined to said other boom element for effecting rotation by the same in opposite directions as said stretches are alternately put into tension upon movement of the structure by the hydraulic means in alternate directions.

3. The invention of claim 2, wherein is included pivot means coupling said stretches on said structure in endtoend and spaced-apart relationship.

4. The invention of claim 2, wherein said hydraulic means includes a pair of piston and cylinder assemblies, said members being mounted on the pistons for reciprocation therewith longitudinally of the cylinders, there being pivot means mounting said members on said structure on opposite sides of said stretches.

5. The invention of claim 4, wherein said stretches are located on said structure in substantially end-to-end and spaced-apart relationship, there being separate pivot mechanisms mounting said cylinders on said one boom element and said members and stretches on said structure for pivotal movement about mutually substantially parellel axes.

6. The invention of claim 5, wherein said structure comprises a plate having a central portion extending between said stretch pivot mechanisms longitudinally of said stretches and interconnecting the same, said plate having a pair of opposed, laterally extending portions mounting said member pivot mechanisms in laterally spaced relationship with respect to said stretches and on either side thereof.

7. The invention of claim 2, wherein is included sheave means rigid with said other element for rotation therewith, said cable being looped around said sheave for rotating the sheave and thereby said other boom element.

8. The invention of claim 7, wherein is included idler pulley means carried by said one member for rotation about an axis substantially parallel to the rotational axis of said sheave means, one of said stretches being looped around said idler pulley means.

9. The invention of claim 7, wherein said cable is wrapped around said sheave for approximately 540", there being means on the sheave and cable for maintaintaining at least a portion of the cable in fixed relative re lationship with respect to said sheave as the latter rotates through an arc of at least 270.

10. The invention of claim 7, wherein is included block means rigid with the stretches at the zone of interconnection therebetween, there being wall means on said sheave means maintaining said block means in a fixed relative position with respect to said sheave means.

11. The invention of claim 10, wherein said sheave has a hub, a central annular web extending radially from said hub and an annular drum located on the periphery of said web, said drum having a pair of circumferentially spaced slots therein extending laterally across said drum, said wall means extending radially of said sheave and being disposed in circumferentially spaced relationship intermediate said slots and between the hub and the drum, said cable being wrapped around said drum and extending continually around said sheave in the same direction, along the outer surface of the drum, through one of said slots, between said drum and hub and through said block means, through the other of said slots and along the outer surface of the drum.

12. The invention of claim 1, wherein is included sheave means rigid with said other element and rotatably carried by said one element, said flexible means including a plurality of side-by-side wire cables trained around said sheave means in a direction for rotating the latter and thereby said other element in response to reciprocation of said members and said structure whereby the diameter of said sheave means and the distance the members and the structure reciprocate to efiect rotation of the other element through a predetermined arc of travel are minimized.

13. The invention of claim 12, wherein said one element includes a pair of elongated, spaced end portions and an elongated insulative section interconnecting the portions, said sheave means, said hydraulic actuation means, said structure and said flexible means being carried by one of said portions in sufficiently spaced relationship with respect to the other of said portions to preclude conduction of electrical current along said boom elements.

14. The invention of claim 13, wherein said portions are spaced sufliciently far to preclude arcing of electrical current therebetween.

15. The invention of claim 14, wherein said portions are longitudinally aligned and said section extends between proximal ends of the portions, said sheave means, said hydraulic actuation means and said cables being located at least as far from said other portion as the proximal end of said one portion.

16. The invention of claim 14, wherein said portions are longitudinally aligned and said section extends between proximal ends of the portions, said sheave means, said hydraulic actuation means and said cables being disposed in non-overlapping relationship to said section.

17. Mechanism for translating the longitudinal movement of flexible cable means in either direction into alternative rotational movement about an axis in opposite directions, said mechanism comprising:

block means rigid with said cable means and located thereon at a zone intermediate the ends thereof;

a sheave mounted for rotation about said axis and having a pair of generally radially extending walls spaced circumferentially of the sheave, said sheave including cable directing means maintaining said cable means in double-looped relationship with respect to the sheave and said block means between said walls;

said sheave including a hub and said cable directing means including an annular web extending radially from the hub, and an annular drum mounted on the outer periphery of the web defining an annular space disposed between said drum and said hub, said wall means being located in said space;

said hub and said drum being elongated in a direction parallel with said axis, said web being located centrally with respect to the hub and the drum and defining a pair of spaces on either side of said web, said cable means including a pair of side-by-side cables, there being a pair of said wall means in each space and block means on each cable, each block means being disposed between the walls of a respective pair of walls.

18. Mechanism as set forth in claim 17, wherein said drum has a pair of circumferentially spaced slots therein disposed on either side of said wall means, said cable be- 9 10 ing wrapped around said drum and extending continuous- FOREIGN PATENTS 1y around said sheave in the same direction, along the 466,884 7/1950 Canada outer surface of the drum, through one of said slots, between said drum and hub and through said block means, OTHER REFERENCES through the other of said slots and along the outer sur- 5 Electrical World, Feb. 16, 1959, p. 93.

face of the drum.

FRED C. MATTERN, JR. Primary Examiner F. D. SHOEMAKER, Assistant Examiner US. Cl. X.R.

References Cited UNITED STATES PATENTS 2,940,539 6/1960 Richey 1822 10 74-89.22;1822 

